Thread grinding machine



Aug. 7, 194:5. s. J. HARLEY ET AL THREAD GRINDING MACHINE Filed Aug. 14, 1942 3 Sheets-Sheet 1 Aug. 7, 1945, s. J. HARLEY ET AL THREAD GRINDING MACHINE Filed Aug. 14, 1942 I5 Sheets-Sheet 2 Aug. 7, 1945. s. J. HARLEY ETAL 2,381,051

THREAD GRI NDING MACHINE Patented Aug. 7, 1945 so sures OFFICE 2 ,3s1,o51= THREAD GRINDING; MAGHINE Stanley Jaffa Barley and John Ernest Wainwright, Coventry; England AipplioationAug-ust 14, 1942, serialiNo. 454,862.

In Great Britain November 7 -1940" 'Thisinvention relates to improvements inand in the production of taps, dies and the likes'crevvthreading tools; I

In the formation of screw threads bymeansof tabs and dies-of the orthodox types the initial operation much more favourable to thetool than to the work-,the conventional tapering off the first tapo'r dieprov-i'ding a strong-thread form towards theleading end designed tomakethe' maximum out at the core" of the work; the amount of cut decreasing progressivelya's the full threadform enters thework.

In use; howevenas is well known; therei'sa heavy resistance tothe initial" enga ement of the first tap or die owing to the taper; the initial part ofthe operation having an action resembling" that oi a reamer and; in the easeof a male tool; such as a tap; setting up a bursting stress intne work piece. Moreover, the form or thecutting; teeth at the leading end of a first tap or die of the orthodoxitype is such as to forrn' a" very wl'aali section at the start of the thread which hasa tendency'to strip and rub:

The rimary object of the present invention is: to obtain a definite and easier engagement" of" the" tool with the work to be threaded by'p'roviding forfa' better control and distribution of the cutting load and a more favourable ratio of initial section ofthread to tha't'of the tool with a proportionate "reduction of the present reamering' efiggflv, 1 i t .7 l

was further obiector the invention is to" form screw-threading tools in;v such a manner that l a greatehpart of the cutting load: is: takeniby the: flank or flanks of the thread on the tool-with a. sidecut. t v a v 1 In the method 0t producing lead on: taps; dies and the like screw-threading tools according-to the present invention relative axial movement between the rotating-flutedblankand the grinding or other thread-formingtool is acceleratedor decelerated in. predetermined: increments betweentlie landsof'saidblank. n V V In order to obtain unilateral cutting-con the leading flank of the thread by the: thread-forming tool, the relative axial movement: between the latter and the rotating: fluted blank-11s retarded between the lands; in pre-determined increments 1 and for such durationhthat cutting threadsareformedv from zero to a,- completelyfull form by the. action of; a multiiorm: tool or wheeL'and-iofa controlling mechanism which: is pre-setatocom plete the taper for the. trequiredi lens-til and: then; cuts out; after which the said; relatives'movementcontinues with. an uninterrupted pitch progressionv To: obtain unilateral cutting on the following flank oil the: thread the operation is similar: ex-

cape-that. inlthiscase the relativelmovement betweeni'th'e blanlri and the: thread-forming tool 1 is accelerated between'the lands.

Bilateral cut-ting on both flanks: is obtained in successive operations: by a; combinationof the two=methods=above described.

In: addition: to the? method above' described: the invention includes the provision of means for carrying the same into practical; effect, said means operating to advancevand/or retard the relative axial'movement between the blank and the" thread-formula tool: to produce a false pitch between: the lands Of a given'length of'the blank anditorproduce a true'pitch. normal to thetap or: clieior therremaining length thereof.

In the accompanying-drawings,

Figure 1 is a side view of the work-head of ascrew -thre'ad grinding machine illustrating one way of carrying out thepresent invention.

FigurerZ: is-a similar viewofgan alternative arrangement-v l t Figure 3 is a longitudinal section through the improved tap? showing progressive increase of leading' flank of thread: i I

liigurefli'v is: a similar View showing; progressive increase of following'flank-of threadi- :Figure: 5 is av similar view showing. progressive increaseion; loo'thv flanksof thread.

Figure 61' illustratesionei ofi the improved taps.

According to the arrangement shown in Figure 1 in: whiclr the: work-head; 2 of; a screw-thread grindingfimacliine.carries and rotates the blank le'ad screw-r engaging a nut: 4 secured to the Wdrle=head=the said nutis 1'-otatab1y mounted: in a lugs on the-- work head and providedw-itn an axial extension carrying" a; pinion 6. This pi'n'ion is rotated to" advance; o'r'reta-rd' the movement of the nut an hence of the worh head relatively to the normalmovement produced by the rota ti'ori oftne. head screw, by means of mechanism including a tam Tand" a ratcl'iet wheel 8 operated fi'oin Said cam: and in geared" relation with ofspun gear I4; The speed of rotation ofthe cam is thus correlated with that of the work-piece. The ratchet wheel 8 is given a stepped rotary movement by the cam I through the agency of a spring-loaded plunger l5 mounted to slide in a bearing l6 carried by the work-head, the plunger having a roller I! at one end bearing against the cam and a pivoted pawl I8 at the other end engaging the ratchet wheel. The motion of the ratchet wheel is imparted to the pinion 6 and hence to the nut 4 at the desired ratio by means of a train of change gears IS. The cam is formed and timed so that during the times the flutes of the rotating blank are passing the grinding wheel the axial or traversing movement of the blank across the grinding wheel is retardedin pre-determined increments by the action of the ratchet wheel on the pinion. .Theduration of retardation is such that cutting threads are formed from zero to a completely full form by the action of a rotating multi-ribbed grinding wheel A shown in dotted lines in Figure 3, the rotating tap blank 2| being traversed in the direction of the arrow. At the stage of the operationzshown, 'thetaper portion ofthe tap has been completed.- Thereafter the ratchet mech anism aforesaid is thrown out of action in the manner hereinafter explained,.and the remaining part of the blank left parallel; the threads to be formed on this part beingindicated in dotted lines at the right-hand of Figure 3. This operation gives a progressive increase on the leading flanks of the thread.

. Alternatively, the cam 1 may be formed and timed so'that duringthe times the flutes of the rotating blank are passing the grinding wheel the axial or traversing movement of the blank is accelerated in pre-determined increments in whichcase the threads are formed from zero to a completely full form with progressive increase on the following flanks, as represented in Figure 4. Y

Bilateral cutting on both flanks of the thread can be-obtained by carrying out the above operations in succession, the result being represented diagrammatically in Figure 5 and by the complete tap in Figure 6.

The duration of the lead control produced by the cam can be controlled in every case by means of a stop adjustably mounted on the ratchet wheel 8 and adapted to throw the pawl I8 out of action when the taper is completed after which the grinding of the thread proceeds in the normal manner with uninterrupted pitch progress1on.' I

In the alternative arrangement shown in Figure 2. the blank 2| may be carried :bya subwork-head 22 slidably mounted on the main workhead 2 and the required acceleration or deceleration in the axial traverse of the blank or workpiece 2| produced by; means of a cam I in co-.

operation witha rack 23 and sine bar 24. In this case the cam is driven from the motor C through the power input shaft II by worm gear 25 through change gears 26 and the telescopic work-spindle [3 by means of a double worm drive 21, 28. The rack 23, which may be suspended rack bears against a slipper pivoted to one rack 23 can be preventedf'from accidental displacement by means of the spring loaded detent 31.

As before, the duration of the acceleration or deceleration-in the traversing movement of the blank is controlled by means of a stop 20 adjustably mounted on the rack and adapted to throw thepawl 34 out of action after which the two work-heads move together under the influence of the lead screw with an uninterrupted pitch progression.

By suitable formation of the sine bar irregular increments of acceleration anddeceleration may be obtained.

Taps and dies produced according to this invention are distinguished from those of the orthodox type in that the pitch of one or of both flanks of the thread varies by predetermined increments from the leading end. In the case of the following flank the pitch increases from the leading end and in the case of the leading flank the pitch decreases in a similar manner.

We claim:

1. Apparatus for producing lead on taps, dies and the like fluted screw-threaded tools comprising a work-head, a work-spindle rotatably mounted therein, a rotating lead screw for. traversing said work-head relatively to a thread-forming tool, ainut rotatably mounted in said work h'e'ad and engaging said lead-screw, a cam rotating cor.- relatively with said work-spindle, a pawl operated by said cam, a ratchet wheel operated by said pawl, and a' train of gears in operative relation between said ratchet Wheel and said nut.

2. Apparatus for producing lead on taps, dies and the like fluted screw-threaded tools comprising a mainwork-head, means for traversing the same relatively to a thread-forming tool, a subworkhead mounted for sliding movement upon said main work-head ,a rotating work-spindle I mounted in said sub-work-head, a tail-stock and spindle mounted in said sub -work-head, means for holding said spindles against relative axial movement, and means operating correlatively with said work-spindle for moving said sub-work-head relatively to the main work-head in the direction of the traversing motion ofthe latter between the actual thread forming operations on the lands of a fluted tap ordie blank rotating with said workspindle.

3. Apparatus according to claim 2 in which the means employed for moving thesub-workhead on the main work-head,' include"acam rotating correlatively with the'work-spindle andmechanism actuated therebyand operating to move the sub-work-head in one direction of traverse against the action of means exerting a'thrust in the reverse direction.

4.'-A machinefor producing'relief in screwthread taps and dies, said machine comprising a work-head adapted to support and rotate the a screw-thread on the lands: of'said work-piece,

' and mechanism for varying the speed of the traversing motion of said head relatively to the speed of rotation of said Work-piece, said mechanism comprising a toothed ratchet element, a cam, a pawl actuated by said cam and actuating said ratchet element, and means for operating said cam.

5. A machine for producing relief in screwthread taps and dies, said machine comprising a work-head adapted to support and rotate the work-piece, means for traversing said head in a direction parallel with the rotational axis of said Work-piece, thread-forming means for producin a screw-thread on the lands of said work-piece, and mechanism for varying the speed of the traversing motion of said head relatively to the speed of rotation of said work-piece, said mechanism comprising a toothed ratchet element, a cam, a pawl actuated by said cam and actuating said ratchet element, means for operating said cam, and a stop adjustably mounted on said toothed ratchet element and moving with the latter into a position wherein it prevents the actuating engagement of said pawl with said ratchet element.

6. Apparatus for producing lead on taps, dies and the like fluted screw-threading tools comprising a main work-head, means for traversing the same relatively to a thread-forming tool, a subwork-head mounted upon said main work-head and carrying a rotating work-spindle, a cam rotating correlatively with the Work-spindle, a rack and sine bar actuated by said cam and operating to move the suh-work-head in the direction of the traversing motion of the main work-head between actual thread formin operations on the lands of a fluted tap or die blank rotating with said spindle, and means for effecting the return movement thereof.

STANLEY J AFFA HARLEY. JOHN ERNEST WAINWRIGHT. 

